Recently, in a semiconductor device manufacturing process, a method referred to as chemical oxide removal (COR) attracts attention as a method for performing micro-etching instead of dry etching or wet etching.
As for the COR process, there is known an etching process for evaporating by-products mainly containing (NH4)2SiF6 (AFS) by heating, the by-products being generated by adsorption of HF gas and NH3 gas on a SiO2 film formed on a surface of a semiconductor wafer as an object to be processed and reaction therebetween (see, e.g., Japanese Patent Application Publication Nos. 2005-39185 and 2008-160000).
Recently, the COR process is applied to etch Si of a poly-Si film or the like using F2 gas and NH3 gas. In that case as well, by-products same as the above by-products are generated and evaporated by heating.
However, in the above etching process, sufficient etching uniformity may not be obtained. Generally, in order to improve the etching uniformity, it is considered to control parameters such as a temperature, a pressure, a gas ratio, gas inlet distribution and the like. However, it has been found that it is difficult to sufficiently improve the etching uniformity by controlling the parameters in such a process that generates by-products having a large molecular mass.